The grain-size dependence of nanoscale ordered regions in Pb(Mg1/3Nb2/3)O3 (PMN) has been studied using
lattice images obtained by transmission electron microscopy. It was found that the size of nanoscale ordered regions, which is
strongly related to dielectric properties, depends on the grain size. The nanoscale ordered regions of fine-grained PMN with
average grain sizes of 0.32 and 0.15 µ m are clearly smaller than those of coarse-grained PMN with an average grain size
of 1.95 µ m. The dielectric constant is found to be markedly low with grain size below ∼0.3 µ m.
Domain wall motion depending on polarization field has been studied for tetragonal lead zirconate titanate (PZT) polycrystals. The domain structure of PZT polycrystals was observed in a backscattered electron image obtained with a scanning electron microscope under various poling conditions. Domain wall reorientation was observed when the applied polarization field strength became higher than the coercive electric field. An in situ X-ray diffraction (XRD) measurement was also done to evaluate the domain wall motion contribution, under a polarization field. The XRD intensity ratio of (002) vs (200) reached as much as 0.72, which was explained by taking the both contributions of domain wall reorientation and translation. The experimental data and consideration by a geometrical domain wall motion model confirmed that the domain wall translation has zero threshold energy and the domain wall reorientation occurs beyond the coercive electric strength, corresponding to a finite threshold energy.
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